This invention relates to a circuit breaker of the puffer type, and more particularly to such a puffer breaker having a pyrolytic cartridge actuating mechanism for opening the contacts of the circuit breaker under fault conditions.
Puffer breakers in which an insulating gas is used as the interruption medium produce a high gas pressure, which is required for interruption of an arc produced by opening of the contacts of the breaker, by adiabatic compression of the insulating gas in the puffer during opening. One advantage of puffer breakers is that no heaters are required to prevent liquefaction of the insulating gas during periods of low ambient temperature, as for example, in breakers using sulfur hexafluoride, SF.sub.6, so long as the pressure within the circuit breaker is kept below approximately 45 psig. A high pressure within the puffer at current zero, the time at which the arc can be most easily interrupted, is desirable, because high gas pressure increases arc cooling performance, thereby increasing the magnitude of current the breaker is capable of interrupting. Another measure of performance improved by use of higher pressure is the magnitude of the initial rate of rise of recovery voltage after current zero which can be withstood by the breaker. However, the higher the pressure required to ensure breaker performance, the larger the mechanical actuation means required to produce such high pressure in the puffer, since the force the actuating piston has to overcome is determined by the pressure difference between the ambient pressure and the pressure inside the puffer. A larger puffer volume and a faster compression of the gas in the puffer during interruption can be used to achieve higher pressure at interruption, but the required high power of the mechanical actuator for such a construction makes this solution costly and inefficient.
Using such large actuating equipment for each breaker operation is inefficient, since the vast majority of circuit breaker openings occur at low current levels, which do not require high pressurization of insulating gas that is required during fault interruption operation. In a particular examination of circuit interruptions, it was found that 3,000 switchings of rated continuous current occured before occurrence of ten interruptions at rated maximum interruption current, i.e., fault interruptions. Therefore, during only 0.3% of puffer breaker openings is the high power required to operate the mechanical actuator under fault conditions needed. Because the same mechanical actuator is used to operate the breaker for normal current operations as for fault current operations, the mechanical actuator must be designed to the specifications of fault current operation. Using the fault current for all breaker operations wastes operating energy, and also produces excess wear of the mechanical actuator.
Prior art attempts to provide the necessary compression of insulating gas include cartridge type circuit breakers as disclosed in U.S. Pat. No. 3,384,724, issued May 21, 1968 to Marx et al. Oil is propelled rapidly by a piston actuated by an explosive cartridge to extinguish an arc drawn between contacts of the circuit breaker. In such structures, the pyrolytic cartridge is detonated at any opening of the contacts to force a flow of coolant over the arc between the contacts. Since this system requires a cartridge opening device for each opening, frequent maintenance will be required for such a breaker.
The prior art includes a circuit breaker using a pyrolytic cartridge for actuation as shown in U.S. Pat. No. 3,281,561, issued Oct. 25, 1966 to Marx et al. This patent illustrates a device for inserting an insulating wall between the opened contacts using a pyrolytic cartridge to move the insulating wall. The insulating fluid used is oil. Another prior art device is illustrated in U.S. Pat. No. 3,264,438, issued Aug. 2, 1966 to Gay in which separation of a connecting bar 21 from conductors 17 and 19 is accomplished using an explosive or gas-forming charge 38 to drive a piston connected to bar 21. Each of these prior art devices employs the same actuating mechanism for every breaker opening.
It is therefore an object of the instant invention to provide high speed, high pressure puffer action to interrupt a circuit at its highest rated current, and to provide in the same device an alternative actuating mechanism for circuit opening at normal continuous current levels.
Another object of the instant invention is to provide a mechanical actuator to operate a circuit breaker under normal continuous current operation, and to provide a pyrolytic cartridge actuator for operating said circuit breaker at maximum interruption current operation.